Not applicable.
1. Field of Invention
This invention relates to solid state imaging sensor assemblies, specifically to a highly compact assemblies of remote head video cameras used in endoscopes, borescopes, laproscopes, diagnostic, inspection and monitoring devices.
2. Description of Prior Art
Medical diagnostic instruments such as endoscopes, gastroscopes, laproscopes, colonoscopes as well as industrial inspection tools like borescopes or monitoring devices, require video cameras of smallest possible dimensions. To achieve this goal remote head cameras are used in which small head with image sensor is separated from bigger video processing circuits. Long and of small diameter cable provides connection and communication between head and processor. Conventional methods of electronic components packaging presently yield imaging sensors measuring approximately 10 by 10 millimeters which defines head assembly cross-section and is far to big for the sophisticated medical and industrial applications. In an effort to reduce imaging sensor size, and allow for smaller remote head of the video camera, an advanced integrated circuits technologies are constantly being developed. One such technology (TABxe2x80x94Tape Automated Bonding) provides leads of the packageless imaging sensor bonded directly to the silicon chip. The leads extend typically outward from two opposite edges of the imager for a distance sufficient to allow the leads to be connected to other components. A transparent window, typically being coated glass, is positioned over the imaging sensor, covering its surface together with the ends of the leads bonded to the silicon chip. Another technology (BGAxe2x80x94Ball Grid Array) produces similar imaging sensors but without leads altogether, with all necessary connections accomplished through small balls of solder formed on the bottom surface of packageless sensor. This class of processes allows reduction of the size of the sensor to approximately 3 by 3 millimeters or less. Imaging sensors of small size like ones described above are structurally week and require special assembly to lend themselves for use in the camera head. Two design configurations of such assembly are known so far, both described in U.S. Pat. No. 5,754,313 to Pelchy et al (1998). First prior art configuration is shown on FIG. 10. The image sensor 110 is centrally mounted upon the shorter edge of an elongated board 111. The imager leads 112, which extend outward from the imager are turned down and are bonded to either side of the board. A plastic resin is applied about the imager package and the board to bond the two together in an assembly. Other electronic components 113xe2x80x94113 are placed on either side of the board 111 to complete the assembly. Transmission cable conductors 115xe2x80x94115 connect this prior art imaging sensor assembly with the camera processing unit and are bonded to the board 111 at the end opposite to the imager 110. Although above described prior art imaging sensor assembly takes full advantage of the small cross-section of the imager, it nevertheless suffers from disadvantage of being unacceptably long. Because of the extended length, this prior art assembly does not lend itself well for the use in medical or industrial instruments, where tip of the instrument, housing the camera, must be articulated to maneuver the device around sharp corners or bends. Second prior art configuration is shown on FIG. 20. The image sensor 210 is mounted on a hybrid circuit board 211 above, and in the parallel alignment to it. Two additional hybrid boards 213 and 214 are placed perpendicularly beneath board 211 in opposite parallel alignment. Electronic circuitry 217xe2x80x94217 is mounted on the inside surfaces of the boards. Encapsulating plastic resin is placed between the boards to provide structural strength to the assembly. The leads 212 extending from the imager 210 are brought down and are bonded to outside faces of the boards 213 and 214. Transmission wires 215xe2x80x94215 being part of the cable which links imaging sensor assembly with processing part of the camera, are bonded to the same outer faces of the hybrid boards just under imager leads 212. This second configuration of the prior art imaging sensor (FIG. 20) assembly attempts to overcome the problem of length in the first configuration (FIG. 10), but brings several new deficiencies.
(a) First weakness is that second prior art imaging sensor assembly has to be build with the expensive hybrid technology not leaving any opportunity to the use of potentially less costly conventional, packaged components, materials or assembly methods. Assembly is composed of three separate hybrids 211, 213 and 214 put together to form one part.
(b) Second, more serious disadvantage, is the placement of a transmission cable conductors 215 on both outer surfaces of the assembly at the end opposed to the imager 210. Starting from the two different places separated by the full width of the assembly, cables are coming together into one bundle some distance from the back of the assembly. This arrangement forms a rigid triangle 220, formed by the back of the assembly and two sets of cable conductors approching from two sides of the assembly. This design is effectively extending bending capabilities of the cable farther away from the assembly. In practice it works like extending length of the assembly some distance behind the physical length of it, effectively nullifying potential advantages of the shorter assembly.
In accordance with the present invention an imaging sensor microassembly compromises of packageless solid state imaging sensor and two boards mounted perpendicularly to each other. Image sensor is mounted in parallel alignment on or above top surface of the top board. Sensor of the type with the leads has them bonded to the opposite edges of that top board. Leadless sensor mounts directly to the surface of the top board. Bottom board is being attached to the other side of the top board, with electronics components placed, space permitting, on the surface of the top board under the imaging sensor. The other components are placed on the one of the surfaces of the bottom board , with the transmission cable conductors attached to the other surface of the bottom board. Bottom board is mounted perpendicularly to the top board not in the center of its surface, but slightly off to one side. This arrangement lives more space to the electrical transmission conductors and allows for the central, symmetrical placement of conductors, lending to best possible bending properties of the assembly.
Accordingly the objects and advantages of the present invention are:
(a) to provide an imaging sensor microassembly which can satisfy size requirements (cross-section and length) of medical and industrial inspection devices like endoscopes or borescopes.
(b) to provide an imaging sensor microassembly which can incorporate microminiature packageless imaging sensor with leads bonded directly to the silicon chip or leadless and, at the same time, will not require, but also not exclude, expensive aterials and components or complicated assembly methods like hybrid technology.
(c) to provide an imaging sensor microassembly with the transmission cables positioned close to the center of the assembly cross-section to allow for the cable to bent in the close proximity to the assembly.
Further object of the present invention is to provide a compact imaging sensor microassembly for video endoscopes, borescopes, laproscopes, diagnostic and monitoring devices that is rugged, insensitive to ambient conditions, simple to use and inexpensive. Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings. These and other objects of the present invention are attained by means of an imaging sensor microassembly suitable for use in the small diameter diagnostic, monitoring and inspection instruments. The assembly includes miniature packageless imager, with the leads bonded directly to the silicon chip or leadless. The assembly includes also two circuit boards. Boards are mounted perpendicularly to each other with the image sensor mounted in parallel alignment to the top surface of the top board. The leads of the sensor are bonded to the two opposite edges of the top board. Leadless sensor mounts directly to the top board. Second, bottom board is attached to the other side of the first board in the pattern resembling capital T, but moved slightly off center to one side. Electronic components are mounted on the surface of the first board under the imager andxe2x80x94or on one side of the second board. The cable conductors are attached to the opposite surface of the second bottom board which is facing towards the center of the assembly. This arrangement puts the cable conductors in the center of the assembly aiding in bending properties of the cables.